The present invention relates generally to an assembly for preventing rapid movement in response to acceleration forces such as earthquakes, between equipment (such as generators, pipes, etc.) and a supporting structure from which the equipment is at least partially supported, while permitting slow movement between such equipment and the structure in response to changes in the temperatures to which the equipment is subjected. More particularly, the present invention relates to an improved snubber assembly for at least partially restraining such equipment and to a method of reducing the number of snubbers utilized in such supporting structures.
In facilities, such as nuclear power generating plants, various pieces of equipment (including, for example, generators, pipes as well as other material handling devices) are utilized for carrying and using high pressure and/or high temperature fluids such as steam, water, sodium and other materials. These pieces of equipment are typically supported (at least in part), spaced from, the walls, floors or ceilings of a building or other surrounding rigid support structures. In geographical areas where frequent earthquakes occur, there is serious concern that such equipment may be damaged during an earthquake because of rapid relative movement due to relatively large acceleration forces between the equipment and the walls, floors or ceilings from which the equipment is supported. This same concern also exists for other "dynamic events" in the equipment which can result in unwanted vibrations or surges, such as water or steam hammer that may occur when there is a sudden opening or closing of valves. Accordingly, there is a current requirement that dynamic restraint devices, i.e., snubbers, be attached between the equipment and the adjacent support structure to prevent or dampen such rapid relative movement during an earthquake or other dynamic event. The equipment must be restrained in such a manner so as to allow the equipment to expand and contract a considerable amount in response to changes in operating temperatures, particularly during start up and shutdown of the facility. The snubbers therefore must permit slow relative movement due to changes in operating temperatures. Each snubber must also be capable of recovering automatically after a dynamic event to once more permit slow movement of the equipment relative to its surrounding support structure.
Each snubber must, of course, be highly reliable, especially because of the expense of providing access, to repair or replace a malfunctioning snubber. Further, since many snubbers are located in high radiation areas during plant operation, the frequent maintenance of such snubbers presents a health hazard to those workers servicing the snubbers. Under guidelines of existing rules and standards, it is still necessary to remove, inspect, test, and reinstall each snubber every five to ten years. The necessary steps to achieve such maintenance are extremely expensive, currently running at about $20,000 per snubber per plant life. Further, since a plant's life is estimated to be about 40 years, such snubbers must each be removed, inspected, tested, and reinstalled severals times over the life of the plant. Since recently built plants contain as many as 2,000 snubbers, or more, it is not difficult to appreciate the relatively large expense necessary to maintain these snubbers.